1. Field of the Invention
This invention relates to a magnetic-tape apparatus comprising a rotary scanning device, a plurality of magnetic heads mounted at the circumference of a rotary body, which heads are associated with rotating amplifiers, a plurality of rotary transformers transferring signals from a stator side to the magnetic heads at a rotor side and vice versa, a device being provided to transmit a signal relating to the rotational phase of the rotary scanning device from the stator side to the rotor side, a device for the generation of a phase-data signal being provided at the stator side of the rotary scanning device, which phase-data signal has a periodically recurring pulse sequence and synchronizes the transfer of signals from and to the magnetic heads, and a circuit for the stepwise transfer being provided at the rotor side of the rotary scanning device, which circuit is resettable by the transmitted synchronization pulse and supplies the head-switching pulses at outputs.
2. Description of the Related Art
In magnetic video tape apparatuses of the helical-scan type, a plurality of rotating magnetic heads successively scan the magnetic tape. In order to avoid interference owing to the fact that playback signals from the magnetic playback heads scanning the helical tracks just recorded are mixed with playback signals from magnetic playback heads currently not scanning the magnetic tape, it is customary (U.S. Pat. No. 4,706,137) to first apply the playback signals just supplied by the rotating magnetic playback heads to a switching device which is controlled by a head-switching signal so as to obtain a continuous playback signal which time-sequentially includes the playback signals produced by the rotating magnetic playback heads. In order to generate the head switching signal a rotational phase detector determines the rotational phase of a rotating drum carrying the rotating magnetic heads. The pulses of a phase signal supplied by the rotational phase detector are delayed in a delay device so as to enable the positions of the rotating magnetic heads to be assigned unambiguously.
Moreover, U.S. Pat. No. 4,905,103 describes a magnetic-tape apparatus with a rotary drum carrying eight magnetic heads at its circumference. In a recording mode the magnetic heads are connected to different amplifier outputs via controlled switches. Frequency dividers are provided to control the controlled switches and are synchronized by a clock signal, locked in phase to the drum rotation, and a reset signal such that the controlled switches are closed groupwise in a given rhythm.
In addition U.S. Pat. No. 4,851,935 describes a rotary scanning device comprising a rotary body which carries not only a plurality of magnetic recording and playback heads and one magnetic erase head but also the amplifiers, controlled switches and control and power supply circuits associated with the individual magnetic heads. For the power supply, to provide an erase signal and to derive a switching signal an additional rotary transformer transmits a modulated 5-MHz signal from the stator side to the rotor side. The transmitted 5-MHz signal is processed at the rotor side to generate switching signals for the various magnetic heads in addition to the supply voltage and the erase signal.
Finally, DE 38 05 438 A1 describes a system for recording and reproducing video signals in which a head disc rotates in the gap between a transversely divided drum around which a magnetic tape is wrapped along a helical path. For writing, reading and erasing the video signals in a manner which allows editing, four magnetic-head groups are 90.degree. spaced apart along the circumference of the head disc and each comprise a normal magnetic playback head, a leading magnetic playback head, a magnetic recording head and a magnetic erase head. The normal magnetic playback heads, the leading magnetic playback heads and the magnetic recording heads have associated amplifiers arranged on the rotating head disc. The amplifiers associated with the rotating magnetic playback heads and recording heads are connected to the rotary transmission devices via controlled switches. The signals required for controlling the controlled switches are derived by means of a control circuit which is also arranged on the rotary head disc and which comprises a number of monostable multivibrators corresponding to the number of controlled switches, the monostables being triggered by the signal from a light barrier.